RESEARCH ARTICLE


Corrosion Behavior of 3% Cr Casing Steel in CO2-Containing Environment: A Case Study



Lin Xu1, 3, Jie Xu2, Ming-biao Xu3, *, Si-yang Li4, Shuai Liu4, Yue Huang3, Fu-chang You5
1 College of Petrochemical and Energetic Engineering, Zhejiang Ocean University, Zhoushan 316022, China
2 Institute of exploration techniques, CAGS, Langfang 065000, China
3 Hubei Cooperative Innovation Center of Unconventional Oil and Gas, Yangtze University, Wuhan 430100, China
4 CNOOC(China) co., Ltd, Shenzhen branch, Shenzhen 518067, China
5 Jiahua Technology Co., Ltd, Jingzhou 434000, China


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© 2017 Xu et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this authors at the Cooperative Innovation Center of Unconventional Oil and Gas, No. 111, Daxue Road, Caidian District, Wuhan, 430100, China; Tel: +8613567661648; Fax: +86 716 8060863; E-mail: xuhu_11@yeah.net


Abstract

Introduction:

The production casing of 3% Cr steel has encountered severe internal corrosion in Huizhou Oilfield. To disclose corrosion behavior of inner casing, a series of corrosion exposure tests were systematically conducted on 3% Cr coupons in terms of in-field conditions.

Material and Methods:

Influence of exposure time, temperature, and water-cut on the CO2 corrosion of 3% Cr steel was investigated, and analyses on weight loss, composition and morphology of corrosion product, and Tafel polarization curves were further carried out.

Result:

The results showed that the corrosion rate of 3% Cr steel increased with increasing temperature, but such trend descended when the temperature exceeded 65°C due to formation of an compact and adherent corrosion product film on the surface of 3% Cr coupons. While varying exposure time from 7 days to 14 days, the corrosion rate decreased, and the Cr and O enrichment was determined in the corrosion products. The corrosion rate of 3% Cr steel increased with a continuous increment of water-cuts, especially when the water-cut was larger than 40%.

Conclusion:

The localized corrosion can happen at the lower water-cut due to the presence of amorphous films. The main corrosion products were FeCO3, Cr5O12, Fe2O3, and Fe-Cr. Entry of CO2 to the simulated formation water caused an increase in the anodic Tafel slope, and accelerated dissolution of 3% Cr steel.

Keywords: 3% Cr steel, Casing corrosion, CO2 environment, Corrosion product film, Water-cut, Tafel polarization curve.